"Sparky", the plasma surface treatment gun
by Graeme W. Gill.
Introduction
Plastic is a wonderfully versatile material to use in making thing. The great diversity of plastic types can be used to advantage in solving all sorts of challenges in engineering and design.While all the traditional means of mechanical fixing can be used to build things out of different plastics, using adhesives often comes with some challenges. While there are some plastics which can be glued together quite easily and reliably, particularly when gluing like to like (i.e. Acrylic to Acrylic, PVC to PVC etc.) many plastics have low surface energy, and do not easily adhere, particularly when attempting to glue different types of plastic together, or gluing to other materials such as metals etc.
In industry, one approach to solving this problem is to use surface treatments, typically flame, chemical, corona or plasma treatments.
Flame treatment can be tricky to get right - it's not really suitable for temperature sensitive materials, and it can be easy to under treat or melt or burn the thing you treating.
Chemical treatment tends to need to be quite specific to the surfaces and adhesives involved, and often the chemicals are not so nice to work with.
Corona and Plasma surface treatments tend to work more broadly, and the nature of this approach suggests that it may be more accessible a maker.
Commercial corona and plasma surface treatment is typically aimed at efficient product production, so high power for high throughput is the main goal. This can make it expensive and complex. The process is also typically optimized for the particular circumstances, with the appropriate choice of equipment and gas.
Inspire by DIY Handheld Gliding Arc Discharge Plasma Surface Treater, I set out to make my own, modest power gliding arc plasma surface treatment gun. This is that project.
Plasma surface treatment
What does plasma surface treatment do ? By creating an electrical arc, air can be ionized, creating a plasma of Nitrogen, Oxygen, Carbon and Hydrogen ions and the freed electrons. By blowing this arc with a stream of air, the ions can be cooled down to form a non-equilibrium plasma, and forcing the arc to glide along the electrodes spreads heat and reduces wear and pitting.Ions created from the breakdown of air initially form into a soup of reactive molecules, that are then able to temporarily modify surface properties, increasing surface energy. This allows better bonding to glues, inks or paints.
Plasma treatment can also be used to clean surfaces such as metals or glass, by combining with and removing surface contaminants.
"Sparky"
The aim here is to make a low power, compact tool for surface treatment of small areas, using readily available parts, allowing professional level gluing of different types of plastics to be achieved at the hobby or maker scale.Using a gliding arc is perhaps the simplest possible approach to creating plasma, and keeping the high voltage electrodes in close physical proximity eliminates some of the high voltage dangers.
Example 1
This example is slightly contrived in the choice of glue and quantity used - two part epoxy glue appears to make a stronger bond than the UV glue for this particular material when treated.
Example 2
A use that perhaps doesn't immediately spring to mind is improving the adhesion of temporary adhesives. Cured silicon is notoriously hard to adhere to, except when using a silicone based adhesive. For this reason it is often used as the basis of adhesive tape carriers, so that the tape can be easily unrolled. Silicone also makes great gaskets, but cutting such a gasket from a sheet of silicone on a CNC cutter can be problematic when it can't easily be held in place.
Even after the plasma treatment, the cutting mat adhesive needs to be in good shape to hold onto the silicone sheet adequately.
Danger - High Voltage!
This project involves high voltage. High voltage should be handled with due respect. You really don't want to be poking around the high voltage circuits in any way that you or anything conductive is within arc distance (20-30mm) when it is turned on. Without the airflow cooling it down, the arc is white hot, and is quite likely to burn you, and anything else it touches.(I measured the maximum current from the high voltage secondary at about 16 mA at 14 Mhz AC, a frequency that literature suggests primarily poses a burn rather than shock hazard. Better off not finding out if this is true though!
If you were to use a different power supply than the one shown here, the hazards may be different.)
License
This design is Copyright Graeme W. Gill 2025, and is made available under the CC BY-NC-SA license.Parts list
| Electrodes | KAI 5028 28mm rotary cutter blade, or make your own out of 0.8mm copper, brass or stainless steel. |
| HV power supply | DC6-15V to AC10kV-25kV 70W Arc Igniter High Voltage Module |
| Fan | 12V 0.15A 5015 Radial Blower fan |
| Fan speed controller | DC12V PWM Fan Governor Speed Control, 2-3/4Wire |
| Push Button | Square 10x10mm, 12mm hole, 23mm long |
| Power socket | DC power line socket, 2.5mm |
| Power supply | 12V 5A/6A AC to DC power supply with 2.5 DC jack |
| Hookup wire | As needed |
| Tinned copper wire | 0.6mm dia, 300 mm |
| M3 Bolts | 10 mm long |
| M4 Bolts | 20mm long |
| M3 Heat set thread | For 3.8mm hole, 3-5mm long |
| M4 Heat set thread | For 4.7mm hole, 4-6mm long |
| 3D Printed parts | Parts A through E, plus the assembly tool F. See STL files and description below. |
Part details
Electrodes
I tried two materials for electrodes; 0.3 mm thick tungsten steel and 0.8 mm thick brass.
Ideally we want a hard metal that will resist erosion from the arc. A high tungsten-copper alloy is ideal, but expensive and not so
easy to get. Another option is tungsten-steel, and I used a KAI 5028 28mm rotary cutter blade <https://kaiscissors.com/product/kai-5028bl-rotary-blade-28mm/> as the basis of these.
The cutter blade is quite hard, but is also thin at 0.3mm thick, and brittle. I cut out two 18.5 x 10 mm sections using a diamond saw in a rotary tool. See (see assets/part_G_thin.stl for the definition of the final electrode shape).
I also cut a small slot to allow attaching the wire, but because the blade is so brittle, I backed it with timber and made sure to
cut into it, to avoid vibration snapping it off. The sharp edge of the cutter ensures a high voltage gradient, reducing the chances of arcing directly across the transformer, but needs to be treated with care during cutting and assembly.
For the brass version, I uses a CNC to cut the shapes and then drilled the 1mm holes, but it should be possible to trace the shape out and cut and finish it manually too. (See assets/part_G_thick.stl)
The electrode edge should be filed to an pointed edge, to increase the voltage gradient, and reduce the chances of arcing directly
across the transformer. Other materials such as stainless steel or copper could also be used.
HV power supply
The High Voltage power supply is a "DC6-15V to AC10kV-25kV Arc Igniter High Voltage Module Lighter 12V Low Heat 20kV" <https://www.ebay.com/itm/205363413486> which at 12V draws up to 5 amps and about 50 Watts. Note that there are several similar looking but different HV modules out there, and they won't work quite the same as this one. When in doubt, check the photo for an exact match.
The fan is a 12V 0.15A 5015 Radial Blower fan, i.e. <https://www.ebay.com/itm/203079798106>
Fan speed controller is a "DC12V PWM Fan Governor Speed Control With Knob 2-3/4Wire Switch Fan Regulation", i.e.
<https://www.ebay.com/itm/403782623271>
The button is a "Pushbutton Push-On Momentary SPST Actuator" Square push button, button 10x10mm, mounting hole Dia 12mm, length 23mm. i.e. <https://www.altronics.com.au/p/s1081-spst-square-momentary-black-solder-tail-pushbutton-switch/> or Round push button, button 12mm, mounting hole Dia 12mm, length 23mm. i.e. PBS-11B <https://www.ebay.com/itm/311599868193> or possibly an Adam Tech SW-PB1-1BS-A-P1-A etc.
DC power line socket, 2.5mm, i.e. <https://www.altronics.com.au/p/p0615-2.5mm-male-dc-power-strain-relief-line-socket/> or <https://www.ebay.com/itm/256441057585> "A" or <https://www.ebay.com/itm/265555305488> "2.5mm Inline"
12V 5A/6A AC to DC power supply with 2.5 DC jack i.e. <https://www.altronics.com.au/p/mb8939d-powertran-12v-dc-6.0a-2.5mm-tip-appliance-powerpack/> or <https://www.amazon.com/ALITOVE-Adapter-Converter-100-240V-5-5x2-1mm/dp/B01GEA8PQA>
etc.
3D Printed parts
The main body of the plasma gun is compose of five 3D Printed parts. A sixth part is a tool to hold the electrodes in place while they are glued.
Part A is the left hand main body, and contains the power socket and hole for the fan speed adjustment.
Part B is the right hand main body, with a cutout for the fan.
Part C is the handle, containing the push button.
Part D is the nozzle.
Part E is the electrode shroud.
Part F is the electrode holder tool, either thin (0.3mm) or thick (0.8mm)
Part G are STL examples of the electrode form for reference, either thin or thick.
(All these files and the Sketchup file they were created from is here.)
I printed all of these from transparent PETG, but only part E, the shroud benefits from a more temperature resistant filament, and something like PLA may be easier to clean up for all the other parts. I printed with a 0.4mm nozzle at 0.2mm layer height, with 3 perimeters and top & bottom layers. The first 3 parts (A, B & C) should be printed with support from the build plate, while the last 3 (D, E & F) should be printed without support.
DO NOT USE carbon or other filament fillings, as this risks arcing between the high voltage wires, and may not provide sufficient insulation to the operator. (PETG has an insulation resistance of about 16KV/mm, so the 4mm of thickness in the design provides about 64KV insulation in total, a comfortable margin over the 20KV that the power supply generates.)
Building and assembling
Print all the 3D printed parts, and clean them up.Add heat set inserts.
Cut and shape the electrodes (see the following photo's for some hints on the details).
Attach 150mm tinned copper wire to corner of each electrodes by winding the wire tightly around the slot/through the hole, and then using conductive glue or appropriate flux to solder the wire. We are after a good mechanical and electrical connections, that will withstand the electrodes getting hot.
Thread the wires through holes in the shroud (Part_E), then position electrodes in the electrode holder tool (Part_F). Check that the whole assembly will fit together smoothly. Disassemble again ready for final assembly.
Apply a release agent to the electrode holder tool (part_G) - I used some petroleum jelly dissolved in shellite (naphtha) or similar solvent. Allow time for the release agent to dry.
Thread the wires through holes in shroud (Part_E), then position electrodes in the electrode holder tool (Part_F), while trying to avoid getting release agent on the electrodes. Lightly spritz the electrodes with water using spray bottle. Slide the whole assembly together again.
Using narrow nozzle or syringe, squeeze some neutral cure RTV silicon into the holes that the wires come out of, until silicon just starts appearing out of narrow cuts in center. As well as holding the electrodes in place, the silicone acts as a thermal insulator, so that the plastic of the shroud is less likely to melt as the electrodes get hot.
Leave silicon to set for at least 24 Hrs.
Carefully remove electrode holder tool.
Clean up the electrodes from any stray silicone.
Clean the top of arc shroud in preparation for gluing, as well as the end of the nozzle.
Thread the leads through the side channels in the nozzle (part_D).
Glue the shroud to the nozzle using (for instance) 2 part epoxy glue, and hold it in place using wire or some other temporary fixing method.
Remove the knob from the fan speed controller.
Test fit all the printed parts and components. Trim the fan housing if needed.
Turn the trim-pot on speed controller PCB fully counter-clockwise.
Remove the electronics, and wire up the parts so that they will fit into place. Solder the push button and DC power connector after passing the wires through the holes. Secure the push button and DC power connect in place using hot glue on the threads. Solder the electrode wires in nozzle to output of the HV transformer, and then slot the nozzle into place as well as re-fitting the rest of the components.
Make sure that the wires are tucked into the housing before completely closing the shell. It may help to hot glue the fan PCB into place, as well as holding the wiring into place. Use the 4mm bolts to hold all the parts together. Add the two 3mm bolts.
Testing and Fan Adjustment
Once it is fully assembled, plug the power in, and turn the speed controller to 80% and make sure that is is running, and air is coming out of the nozzle.Press the button and check that the arc starts, and that there is a blue plasma "flame" coming from the nozzle. (It's probably advisable to not get too close to the plasma with your face though! - use safety glasses.) If there is an arc directly across the transformer, then the electrodes are either not connected or do not have sharp enough edges, or are contaminated in some way. For any other sort of problem, remove the power, disassemble, and visually inspect and debug all the connections before trying again.
Don't enable the arc without any appreciable air flow, because the arc will be hot enough to ignite the plastic of the nozzle shroud (ask me how I know !).
Place the nozzle on a small piece of tissue paper for a few seconds with the arc running, and check that it doesn't cause a burn mark. (It's probably best to do this where the tissue catching alight will not cause a catastrophe! Have some means of putting out handy.)
Turn the fan speed down slightly, and try this again, and repeat. When you get to the point that the tissue shows slight charring due to the plasma, turn it up again, until no charring is visible. (I found that this was about 30-40% of the pot rotation) This seems to be an optimal fan setting, that balances the heat of the arc with maximizing the density of plasma in the air.
Use
First the plasma gun needs to be plugged into the power supply so that the fan can come up to speed.The end of the shroud can then be placed on or very near the surface to be treated, and the arc turned on by pressing the button. The plasma is the purple "flame", and this needs to bathe the surface to be treated. Because this is a modest power device, it should be moved over the surface at a modest pace, typically 10mm/sec or slower. Any faster seems to reduce its effectiveness.
Because the electrodes will heat up while the arc is active, the treatment should be done in bursts of about 15 seconds at a time, with some period between bursts to allow the air stream to cool the electrodes.
The treated surface should be bonded as soon as practical after treatment, as the treatment will wear off with time, the time depending on the nature of the surface.
The effectiveness of the treatment depends critically on the surface type and the the glue being used. It is prudent to try a combination out and assess the resulting strength before applying it to an important project. Even though plasma surface treatment can improve bonding strength by a factor of 3 to 5 times, sometimes the base bonding strength is so low that this is not enough - the resulting bond is still to weak to be useful.
The plasma gun should be used in a well ventilated space, as ozone and other reactive molecules are emitted, and these are not healthy to breath.
This gliding arc form of plasma gun is NOT suitable for use on conductive surfaces such as metals or electronics. If you get it too close to a conductive surface, it will arc over, potentially damaging the surface and/or the shroud of plasma gun. Note that humans are also conductive, and you should avoid the end of the gun coming in proximity to any humans !
A plasma gun suitable for conductive surfaces would have a different electrode arrangement and a swirling air flow.